Propeller



|.. L. ROBERTS.

PROPELLER.

APPLICATION FAILED, APR. 18. 191B.

- Patented Nov. 25, 1919.

2 SHEETS-SHEET I. I

I. L. RDBRTS.

PROPELLER. I APPLICATION FILED APR-18,1918- '31.,823,312 Patented N0v.25,1919.

ISAIAH L. ROBERTS, OF NUEVA GERON'A, ISLE OF PINES, WEST INDIES, ASSIGNOR OF ONE-HALF TO WILLIAM C. LICHTENSTEIN, OF JERSEY CITY, NEW JERSEY.

PROPELLEJR- Specification of Letters Patent.

Patented Nov. 25, 1919.

Application filed April 18, 1918. Serial N0. 229,856. I

To all whom, it may concern:

Be it known that I, ISAIAH L. ROBERTS, a citizen of the United States, residing at Nueva Gerona, in the Isle 'of Pines, West Indies, have invented certain new and useful Improvements in Propellers, of which the following is a specification.

The invention relates to rotary propellers especially suitable for navigation, either marine or aerial, but equally useful in other devices'and machines, such as turbine motors, pumps, blowers, etc. The propeller of the present invention is especially suitable, however, for the propulsion of boats and ships.

Heretofore, practically all of the propellers used'in marine navigation have been designed on the principle of the screw or variations thereof. These forms, as is well known, give an efiiciency of driving-thrust far below one hundred per cent, since no twist of a radial blade has been discovered which will enable the blade in its rotation about a center in passing through the water to produce a theoreticallyperfect thrust at all points thereof at the same time. That portion of the blade near the hub and extending outward to a point approximately half way to the tip yields little or no thrust, according to the speed forward of the vessel, but consumes a considerable portion of the power applied thereto, merely producing a churning action in the water when the speed of the ship is less thanthat for which the twist of the blade is calculated, or acting by its retarding action as a brake if the speed of the ship is higher than that for which the twist given this portion of the blade is calculated. The efiiciency of a blade of a screw-propeller begins at a point some distance from the hub, the distance varying according to the speed of the vessel, and increases gradually to the tip of the blade.

In order to avoid the diiiiculties attending the use of the screw, numerous deviations the principle of the true screw and devised v a propeller along new lines which is of higher efliciency than any now known to me, the high efliciency obtaining alike at high or low speeds, and one in which propelling-thrusts are produced at all points along the working-faces of the blades.

An embodiment. of the invention is illustrated in' the accompanying drawings, wherein- Figure l is a plan view of the propeller;

Fig. 2 is a rear elevation;

Fig. 3 is a rear view in perspective;

Fig. 4 represents a section of one of the blades of the propeller along the line A-B, Fig. 2, somewhat enlarged;

F' 5 shows a similar section through the line --D, Fig. 2;

Fig. 6 shows an enlarged section of the blade along the line EF; and

Fig. 7 is a like section along the line G-H. y

In the drawings, 1 represents the hub or boss of the propeller by means of which the latter is secured on the propelleror driving-shaft of the craft. The blades are indicated at 2 and there are preferably three 7 of them, as shown.

Each of the blades is so shaped that in a rear elevational View, as shown in Fig. 2,

, the leading-edge 3 describes a completesemithe first, and between the two there is formed a semi-circular band terminatlng' at one end in the hub 1 and at the other in the blade-tip 5 which lies in a plane bisecting the hub 1. The center of the circle defined by the leading-edge 3 when viewed from the rear also lies in this plane and at a point half way between the far end of the tip 5 and the far extremity of the alined diameter of the hub.

The frontor thrust-face of the portion of each blade between ,the section line A--B and the boss 1 is uniformly curved, or concave, as shown in Fig. 4. this curvature varying, of course, with the size of the propel er, etc. In the example given, a sixteen inch propeller, which is quite suitable for driving a boat at a speed of ten or twelve miles an hour, is represented, and for a propeller of this size I have found a radius of curvature of one and three-quarters inches, 2'. e. a diameter of three and onehalf inches, to be most suitable. The width of this portion of the blade 2 is determined radius is one-fourth the over-all diameter of the propeller,'four inches 1n the propeller illustrated,and whose center is the center of the hub, intersects the trailingedge 4.

Beyond the line AB, the concavity of the blade 2 diminishes gradually, or, in other words, the curvature flattens more and more as the hub 1 is left, until at the tip 5 there is no curvature and a substantially straight edge results, as clearly appears in Figs. 2 and 3.- Sections through this portion of varying curvatures are illustrated in Figs. l to 7. At AB, Fig. 4, the diameter of the curvature is still three and one-half inches; at CD, Fig. 5, which is half way between A-B and tip 5, the radius of curvature is substantially doubled, so that the diameter here is approximately seven inches; at EF, Fig. 6, which is half way between A-B and C-D, the curvature is the mean of the curvatures at these two sections or approxiinately five and a quarter inches in diameter; while at GH, Fig. -7, the curvature has a diameter of approximately fourteen inches. In other words, the variation in the curvature of this part of the blade is as regular as racticable and increases in the propeller lllustrated from an arc A-B of seventy-five degrees of a circle whose diameter is three and one-half inches to an arc of a circle yvhose diameter is infinity, that is, a straight The portion of the blade from the section AB to the hub 1 lies in the transverse plane of the hub, 2'. e. in a plane at right angles to the axis of the hub, as more clearly shown in Fig. 1. From the section A-B, however, the blade begins to bend rearwardly. The bend is gradual at first but more pronounced as the curvature of the rear face flattens out, until a point about two-thirds of the length of the trailing-edge is reached, approximately along the line CD, Fig. 2, where the bend becomes quite abrupt and makes substantially a rightangle with the initial plane of the blade, when viewed from the top or sides of the propeller, as in Fig. 1. In other words, the portion of the blade from approximately the line AB to the tip 5 is bent backward on a straight incline. The amount of this incline determines the pitch of the propeller or the distance forward it should travel in the water without resistance or slip during one complete revolution, and should be its way unimpeded into the water.

matched with the speed it is intended the boat should have. The inclir-er? portion of the blade should extend, what... ..r the pitch may be, until the tip lies in the plane of the axis'of the hub, as above described, so that the whole blade with its corresponding sector of the hub, when viewed from the rear, defines a semi-circular band. The length of this outer portion of the blade which determines the pitch of the propeller will depend then upon the curvature-gradient of the rear or thrust-face of the blade, and. this in turn varies, of course, with the eifettive area or disk of the propeller.

The angular relation of the curved portion of the blade with respect to the axis of the hub is such that the water acted upon by the curved face leaves the trailing-edge 4 in lines parallel to the axis of the shaft. This being the case, and the arc of the curvature of the blade being less than a quarter circle, the leading-edge will be so disposed as to out To continue the arc of curvature forward to the full ninety degrees would be to lessen the entering or forward-cutting tendency of the leading edge of the blade and to increase the resistance to the passage of the propeller through the water without increasing the propelling action, especially at high boatspeeds, should the propeller-speed not match. Q

The thickness of the blade is much greater at the rear or trailing-edge than at the leading-edge and this thickness diminishes as the tip is approached. The leading edge is comparatively sharp and its thickness varies but little if at all. The increased thickness at the trailing-edge is for. the purpose of strength and rigidity and the degree thereof depends therefore upon the size of the propeller, its dimensions, the power applied,

character of use, etc.

The rear edge 6 of the 'blade adjacent the trailing edge is preferably so located with respect to the trailing-edge 4 that an effect ve water-shed surface 7 is provided for the water leaving the trailing-edge. As shown in Figs. 1 and 3, this is accomplished if this surface in the thicker part of the blade lies in a plane about forty-five degrees from the vertical transverse plane of the hub. The variation in the surface 7 as it leaves the hub and approaches the tip is such that its angular relation with respect to the trailing edge is maintained substantially constant. At speeds less than the normal speed of the ship this surface 7 assists in the propulsion.

It will be understood that the blades, of which there may be two or more, are alike and that the propeller may be either right or left handed.

When the propeller is revolved in the direction of the arrow, Fig. 2, the water strikes the curved faces of the blades and as the latter are so set that the trailing-edges point straight backward, the water is thrust straight backward in lines parallel with the propeller shaft. Likewise, the rearwardly inclined outer part of the blade forces the water straight backward in lines parallel to the shaft. As the thrust forward on the propeller-shaft is equal to the thrust of the water backward, no loss of power occurs except that due to friction of the blades passing through the water.

' It will be obvious to the maker of the propeller that the form and arrangement of the blades must be such that all points of the working-faces thereof will force the water backward in straight lines parallel to the shaft and any deviation from this will be a fault in proportion to such deviation.

- However, variations may be made as to the location of the line AB at which the constant curvature of the working-face of the blade is terminated. For instance, in highspeed boats, the line AB may be farther away from the hub while in low-speed boats it is well to locate it nearer the hub.

The object in curving the portion of the blade between the line AB and the hub in the manner hereinbefore described is to eliminate the churning action usually produced by the blades of the previously known propellers adjacent the hub and to derive an effective forward thrust from the water through which this portion of the blade passes. The portions of the blades near the hub cut through much less water than those portions near the tips and in order to get the same proportional thrust, the water near the hub must'be forced backward on an arc of a smaller; circle than is required near the tips.

It will be noted that the propeller-blade increases in thickness from the relatively sharp leading edge 3 to the rear portion. The strains are taken up by the thicker portion of the blade and the thickness depends therefore largely upon the size of the propeller and the strains which it must withstand. Due to the construction described, I am able to insure considerable strengthin a light propeller, with a consequent saving of a substantial amount of metal.

It will be understood that by the term approximately seventy-five degrees as applied in the claims to the length of are delining the curvature of the thrust-face of the blade, I mean to include arcs of somewhat greater or less lengths and any are of between, say. sixty and ninety degrees is comprehended within the term used. Preferably, however, the arc is appreciably less thana quarter of a circle.

I claim:

1. A propeller-blade, the thrust-face of which has an arcuate concavity the arc of which subtends an angle of approximately I grees.

radius of curvature increasing substantially to infinity at the tip.

2. A propeller-blade, the mathematical projection whereof in the plane of rotation is a semi-circular band, the thrust-face of said blade having a concave portion.

5?. A propeller-blade, the mathematical projection whereof in the plane of rotation is a semi-circular band, the thrust-face of said blade having an arcuate concavity the arc of which subtends an angle of approximately seventy-five degrees.

4. A propeller-blade, the mathematical projection whereof in the plane of rotation is a semi-circular band, the thrust-face of said blade having an arcuate concave portion near the hub the arc of which subtends an angle of approximately seventy-five de- 5. A propeller-blade, the thrust-face of which has an arcuate concavity, the radius of the are being constant in the proximity of the boss of the propeller and progressively increasing in the proximity of the tip of said blade.

6. A propeller-blade, the mathematical projection whereof in theplane of rotation is a semi-circular band, the thrust-face of said blade having an arcuate concavity of progressively increasing radius as the tip is approached, and such portion of the blade being bent backward out of the plane of rotation. l

7. A propeller-blade, the mathematical projection whereof in the plane of rotation is a semi-circular band, the thrust-face of said blade having an arcuate concavity, theradius of the are being constant in the proximity of the boss of the propeller and progressi vely increasing in the proximity of the tip, the portion of the blade having the face of varying curvature being bent backward out of the plane of rotation.

8. A propeller-blade, the thrust-face of which has an arcuate concavity, the radius of the are being constant in that portion of the blade from the boss to a cross-section line approximately midway the length of the blade and. progressively increasing from such line to infinity at the tip of the blade.

9. A propeller-blade, the thrust-face of which has an arcuate concavity. the radius of the are being constant in that portion of the blade from the boss to a cross-section line approximately midway the length of the blade, the arc of this portion subtending an angle of approximately seventy-five degrees, the radius of the curvature progressively increasing from such line to infinity at the tip of the blade.

10. A propeller-blade, the thrust-face of which has an arcuate concavity. the radius of the are being constant in that portion of the blade from the boss to a cross-section line approximately midway the length of the blade, the arc of this portion subtendlng an angle of approximately seventy-five degrees, the radius of curvature progressively increasing from such line to infinity at the tip, and the portion of the blade having the face of varying curvature being bent backward out of the plane of rotation.

11..A propeller blade, the mathematlcal projection whereof in the plane of rotation,

is a semi-circular band, the thrust-face of said blade having an arcuate concavity, the

radius of the are being constant in that portion of the blade from the boss to a crosssection line midway the length of the blade, the arc of this portion subtending an angle of approximately seventy-five degrees, the radius of' curvature progressively increasing from such line to infinity at the tip, and the portion of the blade having the face of length thereof to provide a water-shedding surface.

13. A propeller-blade having a relatively sharp leading edge and a relatively thick rear portion, the under part of said rear portion extending axially beyond the trailing edge substantially along the Whole length thereof to provide a Water-shedding surface, said surface having a constant angular relation to the trailingedge.

In testimony whereof I afiix my signature.

ISAIAH-L. ROBERTS. 

